Abstract: Shear property and water-induced deterioration of discontinuities with different joint wall material (DDJM) play an important role in studies on stability of rock mass and mechanism of geological hazards in the Badong formation. Scanning electron microscope tests and uniaxial compression tests under natural and saturated conditions were firstly conducted on three typical DDJM (silty mudstone / argillaceous siltstone, argillaceous siltstone / argillaceous limestone, and argillaceous limestone / mudstone) to investigate microscopic characteristics of joint walls and water-induced deterioration of the macro mechanical property. Shear properties of these three types of DDJM under natural and saturated conditions were then studied by direct shear tests. A formula to predict the basic friction angle of DDJM was proposed. The results indicate that: 1) the water-induced deterioration of shear property of DDJM is greatly affected by the content of clay minerals and microscopic structure of their joint walls; 2) the basic friction angle of DDJM falls between that of discontinuities with identical joint wall material(DIJM) same with two joint walls of DDJM, and is close to value of DIJM with joint walls same with the softer side of DDJM; 3) the coefficient of water induced deterioration of DDJM is mainly controlled by softening coefficient of the softer joint wall; 4) the coefficient of water-induced deterioration of these three types of DDJM (silty mudstone / argillaceous siltstone、argillaceous siltstone / argillaceous limestone、argillaceous limestone / mudstone) in the Badong formation are 0.915, 0.951 and 0.731, respectively.

Key words: Badong formation, discontinuities with different joint wall material(DDJM), microscopic characteristics, shear property, water-induced deterioration